This invention relates to a module comprising a circuit board and an inductor. For example, the module is a power module which is to be installed in an electronic apparatus to supply electric power. This invention also relates to a magnetic core and an inductor which are suitable for the module.
Generally, an electric component mounted on a circuit board, for example, a switching transistor, a power control Integrated Circuit (IC) or an inductor, generates heat. As the size of the circuit board is reduced, the heat per unit volume increases. Especially, an inductor tends to generate large heat. Accordingly, a module including a circuit board and an inductor is required to have a structure for efficiently radiating heat outward. For example, a module having such a structure is disclosed in Patent Document 1 (USA 2007/0230221), content of which is incorporated herein by reference.
The module of Patent Document 1 comprises an active layer (a circuit board) and a passive layer. The passive layer includes a Low Temperature Co-fired Ceramics (LTCC) inductor made of an LTCC. The circuit board is placed on the LTCC inductor via a heat spreader. Since the module is thus configured, heat generated by the LTCC inductor and the circuit board can be dissipated through the heat spreader.
Patent Document 2 (JP A 2002-289419) discloses a magnetic core formed of soft-magnetic-sintered-alloy layers and insulation layers which are stacked alternately on one another. The content of Patent Document 2 is incorporated herein by reference.
The module of Patent Document 1 is required to include the heat spreader in order to cool the LTCC inductor and the circuit board. Moreover, the module of Patent Document 1 is required to include a heat sink in order to more efficiently radiate the heat generated by the LTCC inductor and the circuit board. In other words, it is necessary to install the members for radiating the heat, namely, the heat spreader, the heat sink and so on, in the module. Accordingly, the module tends to have a complicated structure and a large size. Moreover, ceramics such as the LTCC is a brittle material. Accordingly, the LTCC inductor is easily damaged when pressed against the other member, for example, the member for radiating the heat. Moreover, as described in Patent Document 1, the LTCC inductor has low thermal conductivity. Accordingly, even when the module has the member for radiating the heat, it is difficult to radiate the heat sufficiently.
Moreover, the aforementioned drawback is not limited to the LTCC inductor. In general, although an inductor is a main heat generator in a module, an existing inductor has low thermal conductivity. Accordingly, it is difficult to efficiently radiate the heat generated by the inductor.
When an inductor is formed by using the magnetic core disclosed in Patent Document 2, it is necessary to form a window in each of the soft-magnetic-sintered-alloy layers and to form a through hole in each of the insulation layers. Moreover, it is necessary to stack the soft-magnetic-sintered-alloy layers and the insulation layers in such a manner that the windows and the through holes properly overlap one another. The aforementioned process is cumbersome. Thus, it is not easy to form an inductor having a shape and a size which are suitable for a module.